1. Field of the invention
The present invention relates to variable voltage devices.
2. Description of the prior art
Previously proposed variable voltage devices have included electrical transformers in which the primary to secondary winding turns ratio can be varied by means of sliding brushes.
In these devices the turns of the outer winding are without any insulation over a circumferentially extending area and graphite brushes are slidably mounted to slidably engage the outer winding along the circumferentially extending area. The turns ratio between the two windings of the transformer is thus dependent on the position of the brushes. Such devices are unsuitable for delivering high power because the current which the brushes can support or withstand and the permissible voltage step between adjacent turns are, in practice, limited.
It is an object of the invention to provide a variable voltage device capable of delivering high power.